This invention relates to an assembly and method for a tripping mechanism of an circuit breaker to limit the damage to a protected circuit breaker and other associated equipment such as enclosures, bus way, etc. from the high forces that result from high currents and prevent unwanted tripping of a circuit breaker due to rapidly decreasing currents
Circuit breakers use various trip mechanisms to disconnect the circuit when a pre-determined event has occurred. Often the components of the trip mechanism are required to move at a high velocity as the result of a trip event and impact one another causing stress which can lead to structural or mechanical failure of one of more of the components.
Some circuit breakers use a trip mechanism which includes an electro-magnet which generates high magnetic forces when subjected to high fault currents in a circuit. The magnetic forces attract an armature or other similar component in order to close a gap between the armature and the electro-magnet. Displacement of the armature causes it to travel and impact another component such as a tripbar to continue the tripping sequence. The velocity of the armature travel can result in breaking the tripbar or armature. This is particularly a problem when the components such as the tripbar are made of a plastic material like a high glass thermal set phenoic.
There is a need for limiting the damage to a protected circuit breaker and other associated equipment such as enclosures, bus way, etc. from the high forces that result from high currents. It is also desirable to prevent unwanted tripping of a circuit breaker due to rapidly decreasing currents.
The present invention provides a trip system for a circuit breaker including a sensor to determine a rate of change in the current level. A positive detector is connected to the sensor to determine a positive current direction. A negative detector is connected to the sensor to determine a negative current direction. An electronic switch connected to the positive and negative sensors to activate the tripping mechanism of the circuit breaker. A power supply is connected to the tripping mechanism and electronic switch. Preferably a current delimiter applies a high voltage initially to an inductive device such as a tripping solenoid to effect a quick response but then limit the current to prevent damage to the tripping solenoid.